Ebay would be the first spot to look. There are not reproduction fenders made as of yet, so no luck there. I've been looking for a driver's side fender to salvage the crown for my existing fender. The leading edge made contact with something hard, and has torn and matted the whole tip. I would like to cut off the damaged section and replace it with some original steel. The rest of my fender is in pretty descent shape. It may end up being an excuse to learn how to use an English wheel, and fabricate a new section.
I'd like to find a right side front inner fender wall. The section where the air cleaner sits is in rough shape. Mounting the air cleaner there hasn't done this inner fender wall any favors over the years.